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Science doesn't have all the answers yet to questions about artificial sweeteners

There is no clear evidence that artificial sweeteners cause cancer in humans

Expert: The healthiest people eat a healthy diet and have limited intake of any type of sweetener

Full disclosure: A lot of journalists at CNN drink diet soda. So when we saw a new study suggesting that artificially sweetened beverages are just as bad for you as sugar-sweetened drinks, we, and our readers, bubbled over with questions.

Are artificial sweeteners used in soft drinks and foods safe? Will they make us fat? How much is too much?

Science doesn't have all the answers yet, but we spoke to researchers who had some clues.

Of course, you can always avoid the controversy altogether by replacing soda with water or dessert with fresh fruit. But if you're going to consume artificial sweeteners, we thought you should know the answers to some key questions:

What are artificial sweeteners made of?

There are five FDA-approved artificial sweeteners, and each of them has a different chemical makeup. There's sucralose (Splenda), acesulfame potassium (Sunett, Sweet One), aspartame (Equal, NutraSweet), neotame, and saccharin (SugarTwin, Sweet'N Low).

Aspartame, the sweetener most often used in diet sodas, for instance, is composed of two amino acids: aspartic acid and phenylalanine, according to the American Cancer Society.

Splenda, on the other hand, is created by replacing hydrogen and oxygen in sugar molecules with chlorine atoms.

"It's a taste issue," says Barry Popkin, professor of nutrition at the University of North Carolina's Gillings School of Public Health. "They each have separate taste effects and different people react differently to each of them."

Although consumers may perceive "natural" sweeteners as safer, products such as fruit juices and nectars, molasses, honey and maple syrup frequently undergo processing and refining, according to the Mayo Clinic. The vitamin and mineral content of processed table sugar doesn't differ significantly from these substitutes.

Products such as Stevia, also touted as natural, are also processed and refined before being sold to the public.

What is different is how your body processes artificial sweeteners versus natural ones.

Essentially, the receptors your body uses to detect sweetness are "really awful," according to Eric Walters, author of "The Sweetener Book." In other words, the body's sweet-taste receptor is not very sensitive. It really only detects sugar in large quantities.

But "artificial sweeteners randomly fit the receptor better and it triggers the receptor with far smaller quantities of the material," Walters said. That's why if you were to taste a packet of sugar and a packet of Sweet'N Low, the Sweet'N Low would taste sweeter.

"In fact, in the Sweet'N Low packet there only needs to be a tiny bit of the actual sweet, Sweet'N Low material. It's that sweet -- the rest of it is filler."

Do artificial sweeteners cause cancer?

There is no clear evidence that artificial sweeteners cause cancer in humans, according to the National Cancer Institute. The public's concern seems to stem from older studies that tested the association in rats (not humans) and used extremely high doses of artificial sweeteners.

For example, studies done in the 1970s linked saccharin to bladder cancer in rats, prompting scientists to look into the sweetener's effect on humans. They found the mechanism that caused the cancer wasn't even possible in the human body. Saccharin was removed from the United States' list of carcinogens in 2000.

You may also remember the 1996 study that suggested aspartame was linked to an increase in brain tumors between 1975 and 1992. But a later NCI analysis concluded the increase in brain cancers overall started several years before the FDA's approval of aspartame.

A more recent study, done in 2005, found that when rats were fed high doses of aspartame -- the equivalent of drinking as many as 2,000 cans of diet soda every day -- they had a higher risk of developing lymphoma or leukemia. Would this increased risk still occur in humans with lower doses? Scientists don't think so.

Are sweeteners better or worse than sugar?

"That's where it gets complicated," Walters said. "Different sweeteners have different advantages and disadvantages. If you worry about the calories, then stay away from sugar. If you are most concerned about taste quality, sugar generally tastes best."

Some artificial sweeteners can have small side effects. If you eat too much sorbitol, for instance -- a type of sweetener called a "sugar alcohol" -- it can trigger gas and diarrhea. This is because your body doesn't digest sorbitol as well, Walters said.

Artificial sweeteners contain no calories, so they may aid in weight loss. Yet the new study suggests the lack of calories could also have a counterintuitive effect on the body.

The Purdue University scientists believe the fake sugar in diet sodas teases your body by pretending to give it real food. But when your body doesn't get the things it expects, it becomes confused on how to respond. On a physiological level, they say, this means when diet soda drinkers consume real sugar, the body doesn't release the hormone that regulates blood sugar and blood pressure.

Basically, the healthiest people are those who eat a healthy diet and have limited their intake of any type of sweetener, Popkin said. But if you have a sweet tooth, that may be a hard sell.

So how much is too much?

The FDA recommends ingesting no more than 50 milligrams of aspartame per kilogram of body weight every day. That amounts to 22 cans of diet soda for a 175-pound man, and 15 cans for a 120-pound woman. If you're putting two packets of artificial sugar into coffee, that would be about 116 cups of coffee for the man in this example, and 79 cups for the woman.

"I really think that if you are consuming five or six cans a day, you may have more problems from consuming too much caffeine or acid than from the sweeteners," Walters said.

No large, controlled studies have shown that there is a limit to how much diet soda you can consume without harm if you're keeping the rest of your diet in check, Popkin said. So far, at least, human research has not shown that quantity of artificial sweetener matters.

"It's not whether it's 2 or 6 or 10," Popkin said. "It's a question of what else they do with their diet that counts."

Bottom line?

As with most things in life, artificial sweeteners aren't dangerous in moderation.

Researchers will continue seeking answers to these questions and CNN will continue to report on the latest findings, in pursuit of the soda fountain of youth.